1. Field of the Invention
The invention relates to a molding installation for producing molded parts from plastic in which an extruder unit plasticizes the molding compound such that the compound can be introduced by an injection unit into the mold of a compression-molding unit.
Such molding installations are used to produce molded parts from thermoplastic or thermosetting polymers or elastomers. The polymers may also be fiber-reinforced. The molded parts may be joined to sheets or textiles, in which case a strand of plasticized polymer melt is placed between the opened mold halves of a vertical press and is then press-molded together with the decorative material which has been introduced.
2. Description of the Related Art
European Patent 0 333 198 B1 describes a process in which the polymer melt is introduced into the mold during the closure operation. This has the drawback that the polymer melts which flow together during the compression operation do not join homogeneously to one another at the flow lines, resulting in weak points.
In a known molding installation in accordance with publication WO 97/11829, the polymer melt is plasticized with the aid of a screw plasticizing unit and is deposited in the mold by an injection unit, the injection unit moving backward during the plasticizing operation in accordance with the plasticized volume and the plasticized volume of material being stored in the cylinder chamber in front of the injection plunger. The screw plasticizing unit and injection unit then moves between the opened mold halves. During the return movement of the screw plasticizing and injection unit into its starting position, the injection plunger, by moving forward in the cylinder chamber, forces the plasticized material through a nozzle, the material being deposited into the mold in the form of a strand. The nozzle diverts the melt strand downward through 90.degree. and brings it to the desired discharge width by means of a suitable passage shape. In order, in the case of parts with complicated shapes, to match the melt strand to the shape of the parts as far as possible, the screw plasticizing and injection unit can be moved both laterally and vertically and the nozzle can follow the cavity contour as accurately as possible.
Drawbacks of this molding installation which may be cited are:
The screw plasticizing units may weigh several tons, especially in the case of large volumes of polymer melt, and their speed of movement is therefore limited. PA1 When a plurality of units (for a plurality of parts) are being used, the size of the units means that they impede one another. PA1 When processing fiber-reinforced plastics, it is often necessary to use different screw plasticizing units from the single-screw units which are currently used for injection.